The present invention relates to a method for inspecting a foreign particle or a defect and the like present on a surface of an inspection object, and an apparatus for inspecting the foreign particle, the defect or the like.
In a surface inspection, for example, a circuit is formed by pattern transfer on a bare-wafer and following etching, in a manufacturing process for a semiconductor device. In various manufacturing processes of a semiconductor device for forming a circuit, a foreign particle or a defect and the like attached on a bare-wafer surface accounts for a significant factor of lowering a yield. A foreign particle or a defect attached on a wafer surface is controlled in each step of manufacturing processes, and an apparatus to detect a foreign particle attached on a bare-wafer surface or a defect present on a wafer surface and the like with high sensitivity and high throughput, is a wafer surface inspection apparatus.
Methods to detect a foreign particle or a defect on a wafer surface are mainly classified into methods using a charged particle beam of an electron beam or the like and methods using a light beam, and the methods using a light beam include a method to take an image of a wafer surface by using a camera and analyze image information and a method to detect a scattered light on a wafer surface by a light receiving element like a photoelectron multiplier tube and analyze the extent of light scattering. The latter includes JP-A-63-143830.
In a surface detection apparatus of a method in which a laser beam is irradiated on a wafer, generally a laser beam is irradiated on a wafer surface and a scattered light generated from a foreign particle by the irradiation, is detected by a detector and A/D-converted, and then the size of a foreign particle/defect is calculated from digital data obtained after A/D conversion. To attain high throughput of inspection, a method is adopted that an inspection table, where a work (a wafer) is mounted, is rotated at high speed, and a stage where the inspection table is horizontally mounted in uniaxial direction, is scanned. Based on size information on a foreign particle/defect and coordinate information from the stage, a foreign particle/defect map on an entire surface of the work is calculated.
Aside from a signal generated from a foreign particle/defect of a detection object, reflected light from an inspection object includes a low frequency fluctuation component depending on surface condition, film type or film thickness, and surface roughness. In addition, influenced by vibration or the like from an inspection object movement unit, a low frequency component is generated. This low frequency component is not constant, because it is decided by parameters consisting of a size of illumination light, a speed of the inspection object movement unit and movement position.
Conventionally, though the frequency component was removed or controlled by an analogue filter, since it is difficult for a Cut-off frequency setting to be flexibly varied as being determined by a circuit constant, it was difficult to respond to each of the conditions described above.
In addition, considering distortion of a passing signal, since a passing signal band is required to have a margin, it was hard to have an attenuation frequency band sufficiently wide, and it was difficult for the low frequency component to be removed or controlled accurately.
Accordingly, since a detection determination threshold level has to be raised by the degree of the low frequency fluctuation component remaining after passing the analogue filter, there remained a problem that detection sensitivity was deteriorated by this degree.
In addition, depending on surface condition, film type or film thickness, and surface roughness, reflected light generated from a foreign particle/defect varies itself, therefore there was a problem that it was difficult to respond only with a fixed threshold.